| Much attention has been focused on the study of triplet photosensitizers due to their wide applications in the areas of photocatalysis, triplet-triplet annihilation upconversion and photodynamic therapy and so on. However, the existing photosensitizers have the disadvantages such as inefficient harvesting of visible light and uncontrollable production of triplet excited state, etc. Hence much space has been left on how to design the sensitizers which possess strong visible-light absorbance and triplet state modulation. In this thesis, three series of new photosensitizers were designed and did extensive research on their photophysical properties with steady and time-resolved spectroscopy and DFT calculation. Then they were applied to the photoredox catalytic organic reactions, photodynamic therapy and TTA upconversion, respectively.In order to solve the problem of low efficient utility of visible light, rhodamine was used as intramolecular energy donor and iodo-styryl Bodipy was employed as intramolecular energy acceptor (spin converter). Organic photosensitizers (R-1 and R-2) enhanced with resonance energy transfer (RET) effect was obtained. Both the energy donor and acceptor in R-1 (?= 120000 M-1 cm-1 at 557 nm for the energy donor, and ?= 73300 M-1 cm-1 at 639 nm for the energy acceptor) and R-2?= 89400 M-1 cm-1 at 557 nm and ?= 60400 M-1 cm-1 at 641 nm) show strong absorption in visible region, but at different wavelength. Selectively photoexcitation of rhodamine (energy donor), the singlet energy transfer occurs from rhodamine to iodo-styryl Bodipy (energy acceptor) and triplet excited state is populated via highly efficient ISC in iodo-styryl Bodipy. R-1 was applied to photoredox catalytic organic reactions to synthesize pyrrolo[2,1-a]isoquinoline under mild condition and in the yield of 53%-83%. In addition, R-1 was also applied to photodynamic therapy successfully. Incubated with cancer cells (LLC), the two sensitizers were all localized in the cytosol and most of the cancer cells were killed by the singlet oxygen produced by R-1 after irridiation with 635 nm LED.DTE was employed as photoswitch and 2,6-diiodoBodipy was used as intrarnolecular energy acceptor, organic photosensizer of diiodoBodipyDithienylethene triads (DB-1) was synthesized. Utilizing the competition between ISC in Bodipy and singlet energy transfer from Bodipy to DTE-c, the photoswitching the triplet state of diiodoBodipy was realized. Upon Photoirradiation at 254 nm, the absorbance of the close form (DB-1-c) appeared at around 600 nm, and the process is reversible to the open form (DB-1-o) by the irradiation of the visible light. Especially, selectively photoexcitation with 535 nm, the photoreversion can be accelerated significantly, which identified the existence of the singlet state energy transfer. According to the results of DFT calculation and transient absorption spectra, triplet excited state is localized on 2,6-diiodoBodipy moiety. The photoswitching of triplet photosensitizer was applied to the singlet oxygen photosensitizing (DPBF) and photoswitching triplet-triplet annihilation upconversion which shows good reversibility upon the irradiation of UV and visible light.New heavy-atom free photosensitizer (N-1) was prepared by conjugation 1,8-naphtghalimide (NI) and 2-(2-Hydroxyphenyl)benzothiazole (HBT) which shows obviously red shifted absorption at 405 nm and large stokes shift (up to 140 nm). Long-lived transient species (trans-keto and triplet exited state of cis-keto) were all observed in the transient absorption spectra. |
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